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East Leeds Orbital Route (ELOR) Supplementary G.I.

Tender Value: £340K
Client: Atkins Limited
Engineer: Atkins Limited

50

Rotary Holes 

Rotary drillholes were advanced at the base of the cable percussion holes to recover continuous rock core samples and to provide information on the mine working situation.

53

Boreholes

Cable percussion boreholes weere advanced through the superficial deposits to obtain representative samples of the soils encountered.

16

Trial Trenches

Machine excavated trial trenches were used to assist in determining the extent of previous landfilling.

16

Cone Pentrometer Testing

Static cone penetrometer testing was used in certain areas to yield in-situ parameter information relating to the ground sequence.

PHASE INVESTIGATION SCOPE
Intrusive Site Work53 No. the cable percussive boreholes were advanced into a variable thickness and consistency of superficial cohesive strata (to a maximum depth of 32mBGL), the majority of which were followed by rotary methods into the shallow underlying bedrock (to 36.90mBGL). A coal authority permit was acquired for drilling in areas of known coal seams. In-situ SPT and hand shear vane testing was conducted at specified intervals. The primary purpose was to determine the depth of bedrock including the identification of shallow coal seams. This was to inform foundation design at depth and design of cuttings, embankments and foundations over open cast fill. During drilling, ground gas monitoring was performed as a precautionary measure to assess for noxious/flammable gas and all plant was fitted with spark arrestors. Clean drilling technologies were employed to prevent the downward migration of contaminants. 

104 No. the mechanically excavated trial pits were scheduled to inform carriageway, shallow foundations, earthworks and drainage network elements as well as various geotechnical requirements through soakaway and in-situ testing for soil strength parameters. 

16 No. trial trenches were used to delineate extents of infilled ground and soft ground (alluvium) within the scheme. 
GeologyThe ground conditions in the vicinity of the proposed road corridor were indicated to principally relate to glacial till (predominantly fine grained (cohesive) with silty/granular inclusions)) overlain by patchy near surface alluvium (in connection with localised surface water channels that intersect the scheme. A limited occurrence of made ground (fill) of varying composition and thickness - typically including reworked locally derived superficial deposits/demolition waste/opencast backfill was also proven within places associated with previous mining or developmental interactions. The solid regional geology relates to the Millstone Grit Formation (principally sandstone) evidently weathered intermittently at its upper interface and the Pennine Lower Coal Measures Formation which presented a risk of known/unrecorded mine workings at the southern extent of the site.
MiscellaneousDisturbed/undisturbed sampling techniques.
Hand penetrometer testing.
Field screening of selected environmental soil samples using PID methods to determine SVOC/VOC levels.
Variable/ constant head permeability testing.
Post-works groundwater and gas monitoring in installations over a three month period.
Surveying of all investigation positions.

GENERAL

The proposed scheme comprises a major new orbital road on the north-eastern fringe of Leeds city centre that will serve as a connection between the A6120 outer ring road, near Roundhay Park and Manston Lane (at the southern limit). The intended dual carriageway layout will span over an approximate route of 7km and encroach open undeveloped and agricultural land, commercial-use, infrastructure (including A64 and A58) and natural water features. The project forms part of the East Leeds Extension (ELE) (under the local planning regime of Leeds City Council) involving the redevelopment of 233 hectares of land allocated for residential housing subject to statutory approval and land purchase.

Atkins Ground Engineering were appointed by Balfour Beatty (the Principle Designer for the project) within the role of Investigation Supervisor to implement (in partnership) the detailed design phase of the scheme and were present on site throughout the intrusive works. This study supplements the main ground investigation works performed by Mouchel (in 2015/16).

The initial pre-contract stage involved ensuring that all health and safety information was in place, with Allied Exploration assuming the role of Principal Contractor for the scheme. Detailed Risk Assessments and Method Statements were developed, including a detailed plan illustrating the sequence of the works. Landowners were liaised with to approve access ways and a pre-condition survey was also undertaken in advance of the intrusive works. 

Four cable percussive rigs, three rotary drill units, one subcontracted CPT machine and a contigent of full-time engineers for trial pitting and/or working within the capacity of a supervisory role for delivery of the contract, were allocated to the site. 


INVESTIGATION HIGHLIGHTS

A Client commissioned site survey was carried out in order to delineate any areas with potential environmental constraints, identified exclusion zones and determine the prerequisite for specialist operational controls. Precautionary Method of Works (PMW) were implemented with the liaison of an approved ecologist within areas of protected habitats, during vegetation clearance and to minimise disturbance of invasive species (e.g. Himalayan Balsam) so that exploratory positions were safely located to avoid any potential impact.

An ‘archaeological watching brief’ was maintained during the excavation of specific exploratory holes within the boundary of a former world war I filling factory to mitigate damage to buried relic structural features. For this element of the scheme a ’Scheduled Monument Consent’ (Historic England) was sought which outlined a mandatory suite of conditions for managing the works within the historically sensitive site. Full briefing was provided at the site induction stage to all personnel. Due to the higher likelihood of low level explosive materials (unexploded ordnance) at this former munitions site the Principal Designer commissioned a UXO survey. 

The siteworks were performed to strict protocol under the company’s certified integrated management system to ensure relevant health & safety, environmental and quality objectives were met in line with the Investigation Supervisors requirements.

Post-site activities included long-term monitoring of the gas and groundwater conditions corresponding to the instrumentation installed in the completed exploratory holes.

OUTCOMES

All siteworks were completed in accordance with the Investigation Supervisors objectives to project timescales. The main difficulties experienced during the investigation operations were addressed by a strong management lead, thereby ensuring smooth integration between all operations which were occurring concurrently on-site. Access constraints presented an issue to certain areas of the scheme with some also having inherent hazards that significantly influenced plant movements, i.e. sensitive land-use that required prevention of rutting to ground cover (cropped fields, at the site of the Scheduled Monument), invasive weeds, groundwater management. Steps were taken to avoid cross-contamination between investigation points and a site compound was set-up as a focal point to manage all daily activities.

After completion of the site phase of the investigation the focus transferred into our UKAS accredited geotechnical laboratory which was then tasked with meeting the specified soil testing requirements. Geoenvironmental samples were administered during the site works by the company, however, determinant testing was carried out under a subcontract agreement, including coal tar analysis. Throughout this phase we concentrate on quality, accuracy and data integrity, which is underpinned by our robust quality management system. The same is also true in relation to the report preparation phase and the iterative system we have in place to fully quality check submissions to client organisations.

All data acquired during the investigation finally being issued in a digital AGS compliant format.